A prospective study using two standardized psychological tests, the Profile of Mood States (POMS) and the Self-Rating Depression Scale (SDS), was conducted in an effort to quantify the emotional changes experienced by internal medicine house staff members during the internship. In contrast to instruments used in previous investigations of this type, the POMS and the SDS are standardized tests with proven reliability and validity. The six mood factors measured, “tension-anxiety,” “depression-dejection,” “anger-hostility,” “vigor-activity,” “fatigue-inertia,” and “confusion-bewilderment,” are reported to be among those factors most often affected by the internship experience. Twenty-three interns completed both tests at four-month intervals during one academic year. One-way analysis of variance for repeated measures revealed that the level of only anger-hostility of the mood factors changed significantly during the year. The intensity of this factor increased between the first and third testing periods before dropping at the end of the year. In contrast to findings in previous studies, the depression and fatigue factors did not increase during the year. By characterizing interns' reactions to the stresses of postgraduate medical education, standardized psychological tests can contribute to improved understanding of these reactions and to more intelligent planning of support systems.